This invention relates to an electronic regulating A.C. power controller. More particularly, it relates to such a controller in which different levels of power are manually selectable and regulated through control of trigger on-time control of an electronic A.C. switch interconnecting the A.C. power source and the load.
A number of A.C. voltage regulator circuits are known in which A.C. power to a lamp or other load is regulated through control of an A.C. electronic switch interconnecting the source of A.C. input power, such as standard 120 VAC, 60 Hz, A.C. line power, and the load. Disadvantageously, in some of these circuits regulation is achieved only through a feedback system connected with the load to sense the load power or voltage across the load. This information is used to advance or retard, during each half wave of A.C. power, the time relative to zero crossing, or phase angle, when the electronic switch is triggered into conduction. If the average voltage across the load increases or decreases, the trigger phase angle is advanced or retarded, respectively, and the portion of each half wave of A.C. input power which is applied to the load through the switch is decreased or increased, respectively. Examples of such circuits are shown in U.S. Pat. Nos. 3,538,427 of Oltendorf; 4,300,075 of Foose et al. and 4,359,670 of Hosaka et al. This general type of feedback regulator is also shown and described in G.E. Application Note 200.35, entitled "Using the Triac for Control of A.C. Power", p. 8, published in July 1970 by the Semiconductor Products Department of General Electric Company, Syracuse, N.Y.
While the circuits function to perform as intended, they have a degree of complexity and cost associated with the load sensing feedback circuit which leads to relatively sluggish response and resultant inaccuracies and increase in costs.
At least some of these problems, however, are overcome in A.C. power regulator of Bandou shown in Japanese Pat. No. 58 -106617, published June 25, 1983. In this circuit a microprocessor is employed to eliminate the feedback circuit required in the above A.C. power regulators noted above to reduce the cost, weight, complexity and size of the regulator. This, however, is achieved only at the expense of an analogue to digital converter which converts at least a part, if not all, of each half wave of A.C. input power into digital form. This is used to measure incremental changes reflected in the A.C. input voltage when the power switch is triggered to control the trigger angle of the power switch for regulation purposes. Likewise, in the device shown in U.S. Pat. No. 4,359,670 of Hosaka et al. an analogue to digital converter is required to convert an analogue feedback signal to digital form before it can be applied to a microprocessor used to control the application of load power.
While use of a microprocessor is clearly advantageous over other control devices, analogue to digital converters are relatively expensive and can increase by more than double the electronic component cost of the controller. In U.S. Pat. No. 3,691,452 of Aguiar, a circuit is shown for direct control of load power by a digital signal without the need for an analogue to digital conversion step. Unfortunately, the benefits of a microprocessor are lost in the process and no power regulation is achieved.